Gases, such as steam are commonly condensed into a liquid by flowing them through the horizontal tubes of a heat exchanger. Multiple pass, multi-layered tube designs are usually avoided because the condensed fluid from the first or subsequent passes flows to the bottom of a header where it floods the lowermost tubes. This causes subcooling of the liquid and elimination of the flooded tubes as condensing surfaces. This problem can be avoided by using pairs of tubes connected by U-bends to isolate the fluid in each such pair of tubes. However, the U-bend portions are not readily accessible for cleaning, and leaks are common because of erosion caused by the kinetic energy of the fluid flowing around the bends.